Active mixer resolves local oscillator challenges common to passive designs

Milpitas, CA -- A new RF active mixer from Linear Technology provides linearity and signal-to-noise performance matching that of passive mixers, allowing designers to build 3G cellular basestations that are more compact and at substantially reduced cost. The LT5521 streamlines basestation design by resolving the high LO (Local Oscillator) drive level, poor LO suppression and low conversion gain issues common to passive solutions. In addition to applications in wideband CDMA, UMTS, GSM, and PHS basestation transmitters, the LT5521's low distortion is ideal for cable downlink infrastructure.

The LT5521 incorporates a differential input and output architecture, supporting superior linearity over a wide operating frequency range from 10MHz to 3.7GHz. It also provides flexible operation in either an upconverting or downconverting application. As a transmit (upconverting) mixer, the input third-order intercept (IIP3) is +24.2dBm at 1950MHz, and the Noise Figure (NF) measures 12.5dB. These two parameters contribute to a high spurious-free dynamic range.

Unlike passive mixers, which require a high LO drive level of as much as +17dBm, the LT5521 needs only a modest -5dBm LO signal. This saves one or two stages of external LO amplifier, resulting in a more compact solution size and lower cost. Moreover, the LT5521 offers substantially reduced local oscillator leakage from the LO to other input and output ports. This solves a major design headache by removing undesirable LO signal from the transmit path. Unlike passive mixers, which typically have high conversion loss in the range of 6 to 10dB, the LT5521 has only 0.5dB loss, contributing to improved signal-to-noise performance. Taken as a whole, these attributes result in a solution that has far fewer external blocks, markedly reduced system costs, and overall improved performance.

The LT5521 operates from either a single 5V or 3.3V supply. The device comes in a 16-pin 4mm x 4mm surface mount QFP package. The price in 1,000 piece quantities is $4.95. The product is available from stock.